1. Field of the Invention
The present invention relates to a process for the purification of a styrenic polymer. More particularly, it pertains to a process for efficiently purifying a styrenic polymer having a high degree of syndiotactic configuration in its stereochemical structure of polymer chain to a high level of purity.
2. Description of the Related Arts
Heretofore, styrenic polymers produced by the radical polymerization or the like have had an atactic configuration in stereostructure, have been molded to a variety of shapes by various molding methods such as injection molding, extrusion molding, blow molding, vacuum molding and cast molding and have been used for electrical appliances, office machines, household goods, packaging containers, toys, furnitures, synthetic papers and other industrial materials.
Because of their atactic configuration in stereochemical structure, however, such styrenic polymers have suffered the disadvantage of inferior heat and chemical resistances.
The group of the present inventors has previously succeeded in developing styrenic polymers each having a high degree of syndiotacticity and further, has proved that styrenic polymers having syndiotactic configuration are obtained by the use of a catalyst comprising a titanium compound and a contact product (alkylaluminoxane) of an organoaluminum compound with a condensing agent (refer to Japanese Patent Application Laid-Open No. 187708/1987).
The above-mentioned styrenic polymers are produced by means of slurry polymerization, bulk polymerization or the like and preferably in a high concentration of styrene from the viewpoint of the catalyst activity and polymer productivity. In addition, it has been desired to remove the residual catalyst components in the obtained polymer by means of deashing.
However, the problem still unsolved in deashing was that although the polymer product polymerized at a low conversion efficiency or a low concentration of styrene was easy to deash, the polymer with a high conversion efficiency, for example 60% or higher becomes difficult to deash and clear with increase in the conversion efficiency.
Under such circumstances, intensive research and investigation were made by the present inventors in order to overcome the above-mentioned problem involved in the prior art and to develop a process wherein a styrenic polymer with a high conversion efficiency can be efficiently deashed, that is, the residual catalyst components are efficienty removed so that the polymer is purified to a high level of purity.
As the result, it has been found that the aforestated problem can be solved by subjecting the styrenic polymer to be purified to deashing treatment at a temperature not lower than the glass transition temperature thereof. The present invention has been accomplished on the basis of the foregoing finding and information.